1. Field of the Invention
This invention relates to a film patterning system, and more particularly to a film patterning system having screen molds that are circumferentially stacked one above the other.
2. Description of the Related Art
U.S. Patent Application Publication No. 2007/0196601 discloses a method of making a textured plastic film using a suction roll that includes cylindrical first and second screen elements that are co-axially disposed and that are stacked one above the other for texturing the plastic film guided onto the suction roll.
U.S. Pat. No. 4,543,299 discloses a suction roll or first rotary member having a laminated, seamless, cylindrical metal molding element for vacuum perforation of plastic films. The molding element includes two or more thin geometrically identical, seamless, cylindrical metal screens that are co-axially disposed and that are stacked and bonded together. Formation of the seamless cylindrical metal screens is complicated and expensive. For example, in one method, a mandrel is ground to a dimension corresponding to the desired dimension of the finished metal screen. A desired screen hole pattern is then engraved on the mandrel. A plating resist medium is applied to fill the engraved pattern. A nickel plating is subsequently conducted to form the desired metal screen. The metal screen thus formed is then removed from the mandrel.
In order to obtain a desired perforation pattern on the plastic film, the stacked metal screens are required to be in intimate contact with each other. For example, when two of the metal screens are co-axially disposed and are stacked one above the other, the outer one of the metal screens must have an inner diameter that is substantially equal to an outer diameter of the inner one of the metal screens. As such, a relatively high precision in making the metal screens is required, which results in difficulty in making the metal screens and an increase in manufacturing costs. In addition, assembling difficulties can arise when the metal screens are to be sleeved one over the other.